The present invention generally relates to a band saw machine and, more particularly, to a band saw machine of a type wherein an endless band saw and a stock to be cut are supported for movement relative to each other for effecting the cutting to the stock. The present invention also relates to a method for cutting the stock with the use of the band saw machine.
The band saw machine to which the present invention pertains includes both a type wherein the endless band saw is supported for movement in a direction close towards and away from the stock to be cut and a type wherein the stock is supported for movement in a direction close towards and away from the endless band saw. The first mentioned type is referred to as a saw feed type whereas the second mentioned type is referred to as a stock feed type.
When it comes to the cutting of a stock, for example, a round bar, with the use of the band saw machine of the type referred to above, it is well known that the cutting length of the band saw is minimum at the start and the finish and maximum at the center of the round bar. When the cutting length is small, the band saw is excessively loaded at a local area and the stress built-up takes place at such local area of the band saw, whereas when the cutting length is great and particularly when the cutting is effected at the same speed as that used during the cutting while the cutting length is small, a cutting zone of the band saw is susceptible to an excessive bending stress which ultimately brings about the undue bending of the band saw and, possibly, the breakage of the band saw. Accordingly, it is a general practice that, as the cutting length becomes great, the feed speed of the band saw is reduced to lessen the load acting on the band saw. However, it is also well known that, when the feed speed is reduced in the manner as hereinabove described, saw teeth of the band saw tend to undergo friction relative to the stock beingcut and/or the band saw travelling in one direction is susceptible to a fluttering motion.
As hereinabove discussed, a change in cutting length is accompanied by a change in load acting on the band saw, which in turn brings about the relative friction, between the saw teeth and the stock and/or the fluttering motion of the band saw, thereby adversely affecting the life time of the band saw and also the cutting efficiency. Moreover, this conventional method requires the feed speed to be adjusted with change in cutting length and, accordingly, the automatic adjustment of the feed speed of the band saw can hardly be achieved unless a complicated and expensive control system is employed.
In order to obviate the above discussed problem, it is necessary to keep the cutting length of the band saw relative to the stock to be cut, no matter how great the width of the stock to be cut, within such a range that the band saw may not be adversely affected in the manner as hereinbefore described. In an attempt to accomplish this objective, a band saw machine wherein the band saw undergoes a rocking motion during the cuting of the stock to effect an arcuate cutting has been devised. According to the prior art band saw machine so devised, a frame structure supporting the band saw is supported from above by means of a pair of rocking links inclined in the opposite directions with respect to each other so that the frame structure can be rocked by a cranking mechanism including crank arms in such a way that the opposite ends of the frame structure can be alternately shifted upwards and downwards.
With the prior art band saw machine of the type wherein the band saw undergoes the rocking motion during the cutting operation, since the stock is cut arcuately, the cutting length of the band saw relative to the stock can be kept within the predetermined range regardless of the width of the stock being cut. However, it has been found that not only can the path of movement of the trailing end of the cutting zone of the band saw be rendered arcuate completely, but also the cutting can be performed at equal speed at all times.
In other words, since the stock can not be cut accurately so as to leave an arcuate cut line, the cutting length of the band saw tends to vary more or less. Moreover, even if the band saw is driven so as to travel at equal speed, the feed speed of the band saw relative to the stock varies with the angle of inclination of the band saw and, accordingly, both the cutting length of the band saw relative to the stock and the feed speed of the band saw cannot be kept at a constant value throughout the cutting operation. Furthermore, the band saw as a whole tends to flutter, the necessity has arisen that the cutting reach of the band saw must have a greater length than the maximum width of the stock, and therefore, the machine tends to become bulky having its increased width.